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MySQL Character Set Support

Aug 27, 2004

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3.10 Upgrading Character Sets from MySQL 4.0

Now, what about upgrading from older versions of MySQL? MySQL 4.1 is almost upward compatible with MySQL 4.0 and earlier for the simple reason that almost all the features are new, so there's nothing in earlier versions to conflict with. However, there are some differences and a few things to be aware of.

Most important: The "MySQL 4.0 character set" has the properties of both "MySQL 4.1 character sets" and "MySQL 4.1 collations." You will have to unlearn this. Henceforth, we will not bundle character set/collation properties in the same conglomerate object.

There is a special treatment of national character sets in MySQL 4.1. NCHAR is not the same as CHAR, and N'...' literals are not the same as '...' literals.

Finally, there is a different file format for storing information about character sets and collations. Make sure that you have reinstalled the /share/mysql/charsets/ directory containing the new configuration files.

If you want to start mysqld from a 4.1.x distribution with data created by MySQL 4.0, you should start the server with the same character set and collation. In this case you won't need to reindex your data.

There are two ways to do so:

shell> ./configure --with-charset=... --with-collation=...
shell> ./mysqld --default-character-set=... --default-collation=...

If you used mysqld with, for example, the MySQL 4.0 danish character set, you should now use the latin1 character set and the latin1_danish_ci collation:

shell> ./configure --with-charset=latin1 \
           --with-collation=latin1_danish_ci
shell> ./mysqld --default-character-set=latin1 \
           --default-collation=latin1_danish_ci

Use the table shown in Section 3.10.1, "4.0 Character Sets and Corresponding 4.1 Character Set/Collation Pairs," to find old 4.0 character set names and their 4.1 character set/collation pair equivalents.

If you have non-latin1 data stored in a 4.0 latin1 table and want to convert the table column definitions to reflect the actual character set of the data, use the instructions in Section 3.10.2, "Converting 4.0 Character Columns to 4.1 Format."

3.10.1 4.0 Character Sets and Corresponding 4.1 Character Set/Collation Pairs

ID	4.0 Character Set	4.1 Character Set	4.1 Collation
1	big5	big5	big5_chinese_ci
2	czech	latin2	latin2_czech_ci
3	dec8	dec8	dec8_swedish_ci
4	dos	cp850	cp850_general_ci
5	german1	latin1	latin1_german1_ci
6	hp8	hp8	hp8_english_ci
7	koi8_ru	koi8r	koi8r_general_ci
8	latin1	latin1	latin1_swedish_ci
9	latin2	latin2	latin2_general_ci
10	swe7	swe7	swe7_swedish_ci
11	usa7	ascii	ascii_general_ci
12	ujis	ujis	ujis_japanese_ci
13	sjis	sjis	sjis_japanese_ci
14	cp1251	cp1251	cp1251_bulgarian_ci
15	danish	latin1	latin1_danish_ci
16	hebrew	hebrew	hebrew_general_ci
17	win1251	(removed)	(removed)
18	tis620	tis620	tis620_thai_ci
19	euc_kr	euckr	euckr_korean_ci
20	estonia	latin7	latin7_estonian_ci
21	hungarian	latin2	latin2_hungarian_ci
22	koi8_ukr	koi8u	koi8u_ukrainian_ci
23	win1251ukr	cp1251	cp1251_ukrainian_ci
24	gb2312	gb2312	gb2312_chinese_ci
25	greek	greek	greek_general_ci
26	win1250	cp1250	cp1250_general_ci
27	croat	latin2	latin2_croatian_ci
28	gbk	gbk	gbk_chinese_ci
29	cp1257	cp1257	cp1257_lithuanian_ci
30	latin5	latin5	latin5_turkish_ci
31	latin1_de	latin1	latin1_german2_ci

3.10.2 Converting 4.0 Character Columns to 4.1 Format

Normally, the server runs using the latin1 character set by default. If you have been storing column data that actually is in some other character set that the 4.1 server now supports directly, you can convert the column. However, you should avoid trying to convert directly from latin1 to the "real" character set. This may result in data loss. Instead, convert the column to a binary column type, and then from the binary type to a non-binary type with the desired character set. Conversion to and from binary involves no attempt at character value conversion and preserves your data intact. For example, suppose that you have a 4.0 table with three columns that are used to store values represented in latin1, latin2, and utf8:

CREATE TABLE t
(
  latin1_col CHAR(50),
  latin2_col CHAR(100),
  utf8_col CHAR(150)
);

After upgrading to MySQL 4.1, you want to convert this table to leave latin1_col alone but change the latin2_col and utf8_col columns to have character sets of latin2 and utf8. First, back up your table, then convert the columns as follows:

ALTER TABLE t MODIFY latin2_col BINARY(100);
ALTER TABLE t MODIFY utf8_col BINARY(150);
ALTER TABLE t MODIFY latin2_col CHAR(100) CHARACTER SET latin2;
ALTER TABLE t MODIFY utf8_col CHAR(150) CHARACTER SET utf8;

The first two statements "remove" the character set information from the latin2_col and utf8_col columns. The second two statements assign the proper character sets to the two columns.

If you like, you can combine the to-binary conversions and from-binary conversions into single statements:

ALTER TABLE t
  MODIFY latin2_col BINARY(100),
  MODIFY utf8_col BINARY(150);
ALTER TABLE t
  MODIFY latin2_col CHAR(100) CHARACTER SET latin2,
  MODIFY utf8_col CHAR(150) CHARACTER SET utf8;

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